The following link is a good site to get comparative valuations  

The EVPU will tell you what they are trading for per discovery ounce in the ground. You still need to be careful as there are major differences in grade and potential of individual discoveries.  

http://resourcestockguide.com/comparison_table_page.php?p=1|1|3|0|0|33|0

The companies websites and sec filings are your best bet for more info.